Ground penetrating radar: a brief overview and case study

Harry M. Jol and Derald G. Smith

ABSTRACT

Ground penetrating radar (GPR) is a recently evolving technique for detailed
subsurface investigation of sedimentary environments. Field experiments at over a 100
sites have been conducted over the last year and half. These tests have provided insights
into many areas of Western Canada and United States. The resulting profiles provide high
resolution, continuous subsurface data on facies thickness and depths. The application of
radar stratigraphic analysis (distinct reflection signature patterns) on the collected data
provides both lateral and vertical geometry and stratification of sand bodies under
investigation. Interpretations derived from the radar data coupled with other non-GPR data
(i.e. seismic, borehole data) will aid in understanding the complex nature of depositional
environments and provide useful analogues for comparison with ancient depositional
systems.

Ground penetrating radar was used on the modern lacustrine William River delta,
northern Saskatchewan, to better understand the subsurface sedimentology and reconstruct
former depositional processes (Figure 1). Radar profiling of the wave-influenced sand
deposits along transects up to 3.2 km in length provided high resolution continuous
subsurface data of facies thickness and depths, lithology contacts, dip angle and dip
direction of major sedimentary structures (Jol and Smith, in press; Figures 2 and 3).

A pulseEKKO IV radar system was used with 50 and 100 MHz antennae at a one
metre step for all reflection surveys (Figure 4). Each step location was stacked with a
sampling rate of 800 ps. The profiles were processed and plotted (wiggle trace format)
using pulseEKKO IV software. Near surface velocity measurements were calculated from
CMP surveys (Figure 5). A review of GPR principles and case histories is provided by
Annan and Davis (1977), Beres and Haeni (1991), Davis and Annan (1986, 1988, 1989),
Moorman (1990), Morey (1974), and Ulriksen (1982).

GPR has been found to be a very effective system in assessing subsurface
stratigraphy, depth of lithofacies boundaries and large scale sedimentary structures. The
resulting radar stratigraphy models could have considerable value to the exploration
geophysicists / geologists in the aggregate, placer mining, oil and gas industries. In our
experience, GPR was found to be most effective (resolution and depth of penetration) in
quartzose, dry and/or wet (freshwater), clean (no clay), sandy and gravelly environments
(Jol and Smith, in press). Other subsurface data acquisition methods with similar or
comparable resolution, continuity, portability, cost effectiveness and time efficiency do not
exist when assessing the shallow subsurface (0 - 30 m). Given these conditions, GPR is
unmatched by any other methodology in earth sciences.